Vogel U, Jensen K F
Department of Biological Chemistry, University of Copenhagen, Denmark.
J Biol Chem. 1994 Jun 10;269(23):16236-41.
We measured the transcription elongation rate on two mRNA genes, i.e. infB and lacZ, and on a part of the rrnB gene under conditions when wild type (rel+) Escherichia coli and relaxed (relA) mutants were exposed to isoleucine starvation. The RNA chain growth rates were calculated from the time lag between induction of transcription and the appearance of specific hybridization to probes complementary to the 3' ends of the genes, i.e. from the transcription time. The rate of mRNA chain elongation responded differently in rel+ and relA strains exposed to isoleucine starvation as it decreased (approximately 50%) in rel+ strains that accumulated high concentrations of guanosine 3',5'-bisdiphosphate (ppGpp) and increased (approximately 15%) the relA mutant whose ppGpp pool decayed during starvation. These results show that ppGpp inhibits mRNA chain elongation in vivo. However, stable RNA chain elongation appeared unaffected by ppGpp pool size and was twice as fast as mRNA chain elongation in exponentially growing cells.
我们在野生型（rel +）大肠杆菌和松弛型（relA）突变体暴露于异亮氨酸饥饿的条件下，测量了两个mRNA基因（即infB和lacZ）以及rrnB基因一部分上的转录延伸率。RNA链生长速率是根据转录诱导与与基因3'末端互补的探针出现特异性杂交之间的时间间隔来计算的，即从转录时间来计算。在暴露于异亮氨酸饥饿的rel +和relA菌株中，mRNA链延伸速率的反应不同，因为在积累高浓度鸟苷3'，5'-双二磷酸（ppGpp）的rel +菌株中它降低了（约50％），而在饥饿期间ppGpp库衰减的relA突变体中它增加了（约15％）。这些结果表明，ppGpp在体内抑制mRNA链延伸。然而，稳定RNA链延伸似乎不受ppGpp库大小的影响，并且在指数生长的细胞中是mRNA链延伸速度的两倍。
